A known key-top panel used in a conventional keyboard structure consists of a thin flat layer of an electrically non-conductive material and a plurality of key-top portions protruding from the outer face of the layer and each having an elastic contact element attached to the internal surface of the key-top portion. A typical example of such a key-top panel is taught in Japanese Utility Model Application No. 56-91636. Since the individual key-top portions of the prior-art key-top panel disclosed therein thus protrude from the outer face of the flat layer, the key-top portions tend to be sidewise contacted, pressed or struck by any parts or structures positioned in the neighborhood of the key-top panel or by operator's fingers during assemblage of the keyboard structure or when the keyboard structure having the key-top panel incorporated therein is in use. If the key-top portions are thus contacted, pressed or struck by such members or structures during assemblage of the keyboard structure, the key-top portions of the panel may be scratched or otherwise damaged and might critically impair the external appearances and accordingly the commercial values of the key-top panel and accordingly the keyboard structure.
Because, furthermore, of the fact that the key-top portions of the key-top panel have rounded or otherwise protuberant end surfaces, extra steps are required to have the individual key-top portions temporarily flattened and held in fixed positions to be printed or labeled with alphabetic letters, numerals and/or signs indicative of the specific functions or commands allocated to the key-top portions. Special jigs or other tools or implements have been used to perform such steps, requiring extra costs for the production of the key-top panel and accordingly the keyboard structure using such a key-top panel. If it is desired to have a group of key-top panels manufactured in such a manner as to be distinguishable by the difference of colors from another group of key-top panels, materials colored differently from each other must be respectively used for molding the two groups of key-top panels. This is also responsible for the high production costs of prior-art key-top panels and the keyboard structures using the key-top panels.
Since the key-top portions of a known key-top panel protrude from the outer face of the base layer of the key-top panel as above noted, the key-top portions arranged at certain spacings from one another on the base layer must be reliably separated from one another. For this reason, a frame member used to have the key-top panel supported thereon has not only side and cross will portions but internal partition wall portions adapted to have the individual key-top portions isolated from one another. Provision of such partition wall portions results not only in further increased production costs of the key-top panel and accordingly the keyboard structure using the key-top panel but in deterioration in the compactness and water tightness of the frame member and accordingly of the keyboard structure using the frame member.
The present invention contemplates provision of a useful solution to these problems which have thus far been encountered in a prior-art key-top panel and a conventional keyboard structure using such a key-top panel.